The present invention relates to electrical circuit interrupters, as well as positioning and adjustment of parts in such circuit interrupters.
Electrical distribution and protection equipment is an important element in many applications, particularly those employing medium to high electrical voltages. For example, one such type of equipment is a circuit breaker. Circuit breakers provide protection for electrical systems from electrical fault conditions such as current overloads, short circuits, and low level voltage conditions. Typically, circuit breakers include at least one circuit interrupter, which contains a spring-powered operating mechanism that opens electrical contacts in response to abnormal conditions in order to interrupt the current passing through the conductors in an electrical system. Circuit interrupters are an integral part of not only circuit breakers, but other types of electrical distribution and protection equipment as well.
One particular type of circuit interrupter is a vacuum circuit interrupter, which includes separable main contacts disposed within an insulated and hermetically sealed housing. During the past several decades, vacuum circuit interrupters have gained world-wide acceptance over other technologies for use in circuit breakers, contactors, motor starters, tap changers, distribution reclosers, metal-clad switchgear, and other electrical distribution and protection equipment. Depending on vacuum circuit interrupter construction, vacuum circuit interrupters offer one or more of the following advantages as compared to other types of circuit interrupters: (1) relatively long life due to controlled contact erosion, (2) relatively maintenance-free operation provided by enclosure of the contacts within the hermetically sealed housing, (3) excellent sticking resistance due to the use of hard contact materials, (4) relatively little or no atmospheric contact contamination, which contamination can detrimentally form oxides and corrosion layers on the contacts, (5) relatively little or no noise during operation due to containment of arcing within the hermetically sealed housing, (6) relatively few environmental effects as compared to those interrupters where current interruption does not occur in a vacuum and hence, where greenhouse or toxic gases can be freely emitted into the operating environment, and (7) very low current chop, resulting in a minimal induced transient voltage spike during circuit interruption so that surge suppressors are not required.
Generally, one of the contacts in a vacuum circuit interrupter is fixed relative to both the housing and to an external electrical conductor that is interconnected with the circuit controlled by the circuit interrupter. The other contact is moveable. In the case of a vacuum circuit interrupter, the moveable contact assembly usually comprises a stem of circular cross-section having the contact at one end enclosed within the vacuum chamber, and a driving mechanism at the other end which is external to the vacuum chamber. In one type of vacuum interrupter, an operating rod assembly is provided which carries a rotatable contact bell crank that is slideable on the operating rod and rotates about a pivot pin upon motion of the operating rod. This operating rod assembly is connected to the stem of the moveable contacts. The stem is typically affixed to a bellows seal that maintains the vacuum environment within the chamber while enabling movement of the stem and thus the moveable contact. Motion of the operating rod assembly causes motion of the moveable contact into, or out of, engagement with the fixed contact.
The operating rod assembly is operatively connected to a latchable operating mechanism that is responsive to current. When an abnormal condition occurs, the latchable operating mechanism becomes unlatched, which causes the operating rod to move to the open position. The motion of the operating rod, in turn, causes the contact bell crank to rotate and, as described above, controls the motion of the moveable contact.
Contact springs are typically provided in the operating rod assembly in order to be able to separate the moveable contact from the fixed contact and to ensure the necessary force so that the contacts will not accidentally open under inappropriate conditions. In addition, when appropriate circumstances requiring interruption of the circuit do arise, an adequate force is needed to open the contacts with sufficient speed. If the contacts do not open quickly, there is a risk that the circuit interrupter will fail to interrupt the circuit.
In order to achieve the adequate interrupt speed and force, contact springs are mounted on the operating rod assembly. These contact springs are typically mounted towards one end of the operating rod between the moveable contact and the latchable operating mechanism to provide an over-travel gap (sometimes referred to as a “snatch” gap) or contact wipe portion within the operating rod assembly, a distance through which movement of the springs imparts the necessary speed and force for positioning of the moveable contact. The length of this over-travel gap, or contact wipe portion distance, is determined based on a measure of the force required to hold the vacuum interrupter contacts in a closed position (e.g., against counter forces caused by a peak momentary current). The length of the over-travel gap is also based upon the force required to open the contacts with sufficient speed for safe and clean interruption of an electrical circuit. Therefore, if such springs comprise compression springs, as is typically the case, it is important that the springs have sufficient compression during operation. On the other hand, if tension springs are utilized, adequate tension must exist.
In a typical case, the contact spring is held on the operating rod between a disk-spacer member that is carried along by the operating rod and a shoulder portion of a set of plates that are mounted at one end of the operating rod and spaced apart from the spacer member. When the contacts are closed, the operating rod travels toward its closed position. The plates are slideably mounted on the operating rod in such a way that when the contacts seat, motion of the plates stop. However, motion of the operating rod continues a further distance until it travels to its full extended position. At this point, the contact spring is fully compressed between the spacer member and the shoulder portion of the plates. The further distance traveled by the operating rod is referred to as the over-travel gap (also known as snatch gap) when the operating rod motion is essentially linear or contact wipe portion when the operating rod motion deviates in a non-linear manner with respect to the direction of opening and closing of the contacts. Generally non-linear operating rod motion is associated with those vacuum circuit interrupters that are encased within an open-air system (e.g., fastened to a box in a cantilever arrangement). Linear operating rod motion is associated with those vacuum circuit interrupters that are encased within a closed-air system (e.g., supported by encasement in molded epoxy or another similar material).
In order to ensure that appropriate compression (or tension) is imparted to the contact spring during operation, and hence providing the necessary forces associated with opening and closing the contacts, the over-travel gap is integrated into the circuit breaker design and maintained at a fixed distance. In one typical scenario, when adjustment is needed in order to maintain the fixed distance, repositionable shims are inserted in, removed from, or adjusted within a space residing between the lower end of the vacuum housing (e.g., the plastic bushing surface on the exterior of a vacuum bottle) and the upper end of a support frame (e.g., that provided by a crosshead drive rod or a pole unit support casting). Such shims are identified, for example, in U.S. Pat. No. 4,064,383. FIG. 2 therein illustrates the use of such shims (identified by reference numbers 79 and 80) in adjustment of over-travel gap distance. Special and multiple tools are often required, however, to pry and insert such shims when adjustment is needed. This method is not only cumbersome for users of the circuit breaker, but also ineffective at maintaining precise adjustment of the over-travel gap during operation.
Moreover, due to their repositionability, shims are capable of realigning themselves and even popping out of their intended positions during operation—and often do just that. Circuit breaker users are often ill-equipped to handle needed adjustment and hence vacuum interrupter circuit breakers operated as such often did not work as intended, or required frequent replacement due to the imprecise manner in which they were operated. While adjustment during a circuit breaker's operating life can be needed, due to settling of parts after manufacture and before initial use (e.g., during shipping), adjustment can also be required prior to initial use. In that case, the circuit breaker is adjusted after it reaches, and is positioned within, its destination of intended use.
Thus, more efficient techniques for maintaining or adjusting over-travel gaps and contact wipe portions in operating rod assemblies of circuit interrupters are needed. Not only is reliability desired in that regard, but ease of adjustment is also desired.